Re: arsclist Re: 45 rpm record groove depth

[Graham Newton <gn@xxxxxxxxxxxxxxxxxxxxx>]

Chuck Howell, CA
Curator, Library of American Broadcasting
Hornbake Library
University of Maryland
College Park, MD  20742
(phone) 301-314-0401
(fax) 301-314-2634

Chuck Howell wrote:

> Does anyone out there in listserve land happen to either
> know the depth of a 45 rpm microgroove or know where I can
> find this information?  This question was posed to us by a
> researcher, and we haven't been able to track it down.
> Width yes.  Depth no.

Styli used to cut the grooves will determine the depth for a given width
measurement which is usually taken by a calibrated graticule microscope
looking at the edges of the land across the groove.  A small included angle
at the stylus tip will result in greater groove depth whereas a larger 
included angle will result in a lesser groove depth.  Most 45's were cut 
with the same stylus that LP's were cut with, the only difference being 
setting to a greater groove width (and hence increasing the depth) to allow
for the higher recorded levels on the pop music discs that were being cut.
The included angle of the grooves were specified as 90 degrees +/- 2 degrees.
You'll get a good idea of the depth from that, less the radius of the cutting
stylus tip.  


... Graham Newton

-- 
Audio Restoration by Graham Newton, http://www.audio-restoration.com
World class professional services applied to phonograph and tape
recordings for consumers and re-releases, featuring CEDAR processes.